Hearing aids are electronic instruments worn in or around the ear that compensate for hearing losses by amplifying sound. Because hearing loss in most patients occurs non-uniformly over the audio frequency range, most commonly in the high frequency range, hearing aids are usually designed to compensate for the hearing deficit by amplifying received sound in a frequency-specific manner. Adjusting a hearing aid's frequency specific amplification characteristics to achieve a desired optimal target response for an individual patient is referred to as fitting the hearing aid. One way to determine the optimal target response of the hearing aid is by testing the patient with a series of audio tones at different frequencies. The hearing deficit at each tested frequency can be quantified in terms of the gain required to bring the patients hearing threshold to a normal value.
Fitting a hearing aid by threshold testing discrete tones, however, is not entirely satisfactory. Since it is practical to threshold test at only a few discrete frequencies, the frequency response of the hearing aid is adjusted only at those frequencies. Sounds in the real world such as speech, however, are complex waveforms whose components may vary more or less continuously over a relatively wide range in the frequency domain. Modern digital hearing aids also incorporate signal processing functions such as noise reduction and frequency translation in order to provide better compensation for a particular patient's hearing loss. It would be desirable to provide the patient with information reflective of how the hearing aid is processing sound so that hearing aid parameters can be adjusted during the fitting process using feedback from the patient.